feat: Add IESG decisions to the IESG group menu

[evyncke]

As the IESG just (re)-discovered the "IESG decisions" endpoint and as it is useful for the community, adding it to the IESG-specific sub-group menu.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.53%. Comparing base (4641d0d) to head (08e1c48).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11050      +/-   ##
==========================================
+ Coverage   88.51%   88.53%   +0.01%     
==========================================
  Files         334      334              
  Lines       45102    45109       +7     
==========================================
+ Hits        39924    39935      +11     
+ Misses       5178     5174       -4     

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